1. Field of the Invention
The present invention relates to device calibration and characterization and, more particularly, to using a multi-step process wherein a data store is accessed during the process to retrieve and update the data therein and/or to determine a measurement status usable in identifying an initiation point, the data store including such data as device control signals, position information associated with color patches in a target image, and device measurement values used to characterize a color device.
2. Description of the Related Art
Computing systems use different types of input and/or output devices to reproduce colors in, for example, a color, or graphics, image. A color may be interpreted or represented differently depending on the device. For example, a camera may understand a given color red as its red “500” while the color that is displayed by a monitor when it is asked to generate the same red “500” corresponds more closely to a red “325”. Device characterization is a process used to map device colors to a set (or sets) of standard, or reference, colors. Using the mapping obtained by characterizing a color device, it is possible to predict the actual color reproduced by the device to provide a consistent color reproduction across devices.
Using the conventional model for characterizing a color device, a target image is used that includes a collection of colored patches that represent a sampling of the colors that the device is expected to support. In the case of a printer, this is a set of printed sheets generated by the printer. In the case of a monitor, this is a set of displayed colors. In the case of a scanner, it is a target document that contains the color patches that is printed using some technology that is likely to be used with the scanner (e.g., photographic print film).
There is currently no universal format for target images for use with color devices regardless of the device type. In the case of scanners, there are multiple standard formats for target images, called ‘IT8s’, each of which is used with a particular print technology such as color print film, transparency film and 4-color print. However, these target image format are not intended for use with other color devices such as printers and/or monitors. In fact, there is currently no target image standard for use with such color devices.
Each IT8 target is therefore only useful for a particular print technology for use with scanners and other color input devices. Further, since the IT8 targets are produced by the manufacturers of the print technology, the target images are closely tied to the print technology with little or no regard to a scanner's other capabilities beyond those used with the particular print technology. This may result in only a limited part of the scanner's capabilities being addressed in the IT8 targets.
In the conventional characterization model, each of the color patches in a target image is measured using a standardized color measurement device (e.g., calorimeter or spectrophotometer). The resulting data is used, along with device control signals associated with each of the patches, to produce the device characterization. For a printer and monitor, for example, the device control signals are the signals used to generate the printed sheets and the displayed colors, respectively. For a scanner or other input device, the device control signals are the signals generated by the scanner as a result of scanning the target image containing the patches.
As with target image formats, there is currently no universal approach for storing measurements produced during the measurement process. With respect to scanners, there is a standardized data format that may be used to retain measurement data produced from an IT8 target image. The standardized data format, which is defined in an IT8 specification (available from the American National Standards Institute), defines a format for storing measurement data only. That is, there is no provision in the standard for retaining scanner control signals or other information associated with the measurement process. There is currently no standard for storing measurement data associated with printers and/or monitors.
To store scanner measurement data, there are currently three standard data formats each of which is used with different IT8 target images to store measurement data only: (1) the IT8.7/1 for use with transparency film; (2) the IT8.7/2 is used with print film to store measurement data; and (3) the IT8.7/3 standard for use with 4-color print.
FIG. 1 contains an example of a file using the IT8 standard to store measurement data associated with an IT8.7/1 (i.e., transparency film) target for use with scanners. The first three lines are part of a header and provide general descriptive information. The next five lines identify the syntax of the data portion of the file. That is, the number of rows of data (i.e., “NUMBER_OF_SETS”), the columns or fields within a row (i.e., “NUMBER_OF_FIELDS”) and the corresponding field name associated with each field in the row (i.e., “SAMPLE_ID,” “XYZ_X,” etc.). The data portion of the IT8 file identifies the measurements obtained from scanning the target image.
The measurement values stored in the IT8.7/1 data file of FIG. 1 and the control signals obtained from the scanner as a result of scanning the corresponding IT8 target image may be used to generate a scanner profile (e.g., a profile that conforms with the International Color Consortium, or ICC profile) that takes into account the specific characteristics (e.g., the measurements) of the device. However, since the IT8.7/1 standard is used with a transparency print file target image, the scanner profile is limited to only this technology.
As discussed above, the characterization of a device is a multi-stage process including producing a target image and measuring the color patches in the target image. The process of producing a target image and measuring color patches in the target image is often times very time consuming as a target image may comprise may hundreds or thousands of patches.
However, it may be determined that an error occurred during the measurement. Using the conventional model, it is necessary to repeat the entire process. For example, the measurements obtained may be flawed due to flaws in the target image medium (e.g., a wrinkle or tear in the medium). It may be determined that additional patches are needed to take into account more measurements in a given range of the color spectrum. Alternatively, it may be that the process did not complete because it was interrupted for some reason (e.g., a hardware crash).
Further, it may be that multiple target images are needed to characterize a color device. For example, as discussed above, in the case of scanners, there are target images for print film, 4-color print and transparency technologies. However, scanners are typically intended for use in a general purpose environment in which other types of output medium or ink may be used. Also, it may be that a scanner may have a wider color range than can be supported by any single output device. Using the current approach, a different target is produced and a separate characterization process is performed for each target.
Under the current approach, there is no standardized mechanism for use with all types of color devices. Further, there is no ability to determine which, if any, portion of the measurement process is to be performed to avoid repeating the entire process. In addition, there is no ability to retain measurement information in a single location.